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wireless telegraphy has made such enormous strides and has
advanced to such a degree of perfection； one naturally would
conclude that it constitutes an ideal system of communication
under such conditions in military operations。
But this is not the case。 Wireless is utilised only to a very
limited extent。 This is due to two causes。 The one is of a
technical； the other of a strategical character。
The uninitiated； bearing in mind the comparative ease with which
wireless installations may be established at a relatively small
expense； would not unreasonably think that no serious
difficulties of a technical character could arise： at least none
which would defy solution。 But these difficulties exist in two
or three different fields； each of which is peculiarly complex
and demands individual treatment。
In the first place； there is the weight of the necessary
installation。 In the case of the dirigible this may be a
secondary consideration； but with the aeroplane it is a matter of
primary and vital importance。 Again； under present conditions；
the noise of the motor is apt to render the intelligent
deciphering of messages while aloft a matter of extreme
difficulty； especially as these are communicated in code。 The
engine noise might be effectively overcome by the use of a
muffler such as； is used with automobiles； but then there is the
further difficulty of vibration。
This problem is being attacked in an ingenious manner。 It is
proposed to substitute for audible signals visual
interpretations； by the aid of an electric lamp； the fluctuations
in which would correspond to the dots and dashes of the Morse
code。 Thus the airman would read his messages by sight instead
of by sound。
This method； however； is quite in its infancy； and although
attractive in theory and fascinating as a laboratory experiment
or when conducted under experimental conditions； it has not
proved reliable or effective in aeronautical operations。 But at
the same time it indicates a promising line of research and
development。
Then there are the problems of weight and the aerial。 So far as
present knowledge goes； the most satisfactory form of aerial yet
exploited is that known as the trailing wire。 From 300 to 700
feet of wire are coiled upon a reel； and when aloft this wire is
paid out so that it hangs below the aeroplane。 As a matter of
fact；when the machine is travelling at high speed it trails
horizontally astern； but this is immaterial。 One investigator；
who strongly disapproves of the trailing aerial； has carried out
experiments with a network of wires laid upon and attached to the
surface of the aeroplane's wings。 But the trailing wire is
generally preferred； and certainly up to the present has proved
more satisfactory。
The greatest obstacle； however； is the necessary apparatus。 The
average aeroplane designed for military duty is already loaded to
the maximum。 As a rule it carries the pilot and an observer； and
invariably includes a light arm for defence against an aerial
enemy； together with an adequate supply of ammunition； while
unless short sharp flights are to be made； the fuel supply
represents an appreciable load。 Under these circumstances the
item of weight is a vital consideration。 It must be kept within
a limit of 100 pounds； and the less the equipment weighs the more
satisfactory it is likely to prove； other things being equal。
The two most successful systems yet exploited are the Dubilier
and the Rouget。 The former is an American invention； the latter
is of French origin。 Both have been tested by the British
Military Aeronautical Department； and the French authorities
have subjected the French system to rigorous trials。 Both
systems； within their limitations； have proved satisfactory。
The outstanding feature of the Dubilier system is the production
of sine waves of musical frequency from continuous current； thus
dispensing with the rotary converter。 The operating principle is
the obtaining of a series of unidirectional impulses by a
condenser discharge； the pulsating currents following one another
at regular intervals at a frequency of 500 impulses per second；
which may be augmented up to 1；000 impulses per second。 The
complete weight of such an apparatus is 40 pounds； the electric
generator； which is no larger than the motor used for driving the
ordinary table ventilating fan； accounts for 16 pounds of this
total。 Under test at sea； upon the deck of a ship； a range of
250 miles has been obtained。 The British Government carried out
a series of experiments with this system； using a small plant
weighing about 30 pounds； with which communication was maintained
up to about 20 miles。
In the French system the Reuget transmitter is employed。 The
apparatus； including the dynamo； which is extremely small； weighs
in all 70 pounds。 A small alternator of 200 watts and 100 volts
is coupled direct to the aeroplane motor； a new clutch coupler
being employed for this purpose。 By means of a small transformer
the voltage is raised to 30；000 volts； at which the condenser is
charged。 In this instance the musical spark method is employed。
The whole of the high tension wiring is placed within a small
space so as not to endanger the pilot； while the transformer is
hermetically sealed in a box with paraffin。 The aerial comprises
a trailing wire 100 feet in length； which； however； can be
wound in upon its reel within 15 seconds。 This reeled antenna；
moreover； is fitted with a safety device whereby the wire can be
cut adrift in the event of an accident befalling the aeroplane
and necessitating an abrupt descent。 With this apparatus the
French authorities have been able to maintain communication over
a distance of 30 miles。
In maintaining ethereal communication with aeroplanes； however； a
portable or mobile station upon the ground is requisite； and this
station must be within the radius of the aerial transmitter； if
messages are to be received from aloft with any degree of
accuracy and reliability。 Thus it will be recognised that the
land station is as important as the aeroplane equipment； and
demands similar consideration。
A wide variety of systems have been employed to meet these
conditions。 There is the travelling automobile station； in which
the installation is mounted upon a motor…car。 In this instance
the whole equipment is carried upon a single vehicle； while the
antenna is stowed upon the roof and can be raised or lowered
within a few seconds。 If motor traction is unavailable； then
animal haulage may be employed； but in this instance the
installation is divided between two vehicles； one carrying the
transmitting and receiving apparatus and the generating plant；
the other the fuel supplies and the aerial； together with spare
parts。
The motive power is supplied by a small air cooled petrol or
gasoline motor developing eight horse…power； and coupled direct
to a 2…kilo watt alternator。 At one end of the shaft of the
latter the disk discharger is mounted； its function being to
break up the train of waves into groups of waves； so as to impart
a musical sound to the note produced in the receiver。 A flexible
cable transmits the electric current from the generator to the
wagon containing the instruments。 The aerial is built up of
masts carried in sections。
The Germans employ a mobile apparatus which is very similar； but
in this instance the mast is telescopic。 When closed it occupies
but little space。 By turning the winch handle the mast is
extended； and can be carried to any height up to a maximum of
about 100 feet。 The capacity of these mobile stations varies
within wide limits； the range of the largest and most powerful
installations being about 200 miles。 The disadvantage of these
systems； however； is that they are condemned to territories where
the ground at the utmost is gently undulating； and where there
are roads on which four…wheeled vehicles can travel。
For operation in hilly districts； where only trails are to be
found； the Marconi Company； has perfected what may be described
as 〃pack〃 and 〃knapsack〃 installations respectively。 In the
first named the whole of the installation is mounted upon the
backs of four horses。 The first carries the generator set； the
second the transmitting instruments； the third the receiving
equipment； and the fourth the detachable mast and stays。
The generator is carried upon the horse's saddle； and is fitted
with a pair of legs on each side。 On one side of the saddle is
mounted a small highspeed explosion motor； while on the opposite
side； in axial alignment with the motor； is a small dynamo。 When
it is desired to erect the installation the saddle carrying this
set is removed from the horse's back and placed upon the ground；
the legs acting as the support。 A length of shaft is then
slipped into sockets at